A field-emission cathode (or field emitter) contains a group of electron-emissive elements that emit electrons upon being subjected to an electric field of sufficient strength. The electron-emissive elements are typically situated over a patterned layer of emitter electrodes. In a gated field emitter, a patterned gate layer typically overlies the patterned emitter layer at the locations of the electron-emissive elements. Each electron-emissive element is exposed through an opening in the gate layer. When a suitable voltage is applied between a selected portion of the gate layer and a selected portion of the emitter layer, the gate layer extracts electrons from the electron-emissive elements at the intersection of the two selected portions.
In fabricating a field emitter, there are normally multiple instances in which one segment of a coating needs to be spaced apart from another segment of the coating. Various conventional techniques are available for achieving the desired separation between the coating segments.
For example, the coating can be deposited as a blanket layer and then photolithographically patterned to remove part of the blanket layer, thereby creating the separation. However, the field emitter may occasionally become contaminated or otherwise damaged by the photolithographic patterning materials, including (a) the photoresist used to cover the coating segments intended to remain in the structure after the patterning operation, (b) the photoresist developer employed to remove the photoresist above where part of the blanket layer is to be removed, and (c) the etchant utilized to remove that part of the blanket layer. Also, the photolithographic masking technique typically does not work well over surfaces having rough topography.
Another conventional technique is to selectively deposit the coating material using a mask, commonly termed a shadow mask, situated above the field emitter to prevent the coating material from accumulating on areas where no coating material is desired. By using the shadow masking technique, the likelihood of contaminating or otherwise damaging the field emitter is normally reduced to a low level. Unfortunately, the shadow masking technique normally cannot be utilized to accurately define fine (or small) features, especially features of the fineness typically needed in the active area of a field emitter. It is desirable to have a technique for providing a coating in multiple finely defined segments over a relatively rough surface of a field emitter.